Obesity is occurring at epidemic rates not only in United States of America but all around the World. According to the World Health Organization report, more than one billion adults (˜15% of world population) are overweight (body mass index (BMI>25), over 300 million adults are truly obese (BMI>30) and these numbers are expected to increase by more than half again by the year 2025 (Tseng et al. Nat Rev Drug Discov. 2010; 9(6): 465-482). Obesity represents a major risk factor for the development of many of our most common medical conditions, including diabetes, insulin resistance, dyslipidemia, non-alcoholic fatty liver, cardiovascular disease and even some cancers (Haslam et al. Lancet. 2005; 366(9492):1197-209; Bhatia et al. Curr Opin Cardiol. 2012; 27(4):420-8). Accordingly, the economic impact of obesity continues to rise steeply. Obesity develops from perturbation of cellular bioenergetics, when energy uptake exceeds energy expenditure (Kajimura et al. Cell Metab. 2010; 11(4):257-62; Nedergaard et al. Cell Metab. 2011; 13(3):238-40). While most obesity therapies are focused on reducing caloric intake and exercise (Isidro et al. Mini Rev Med Chem. 2009; 9(6):664-73; Grundy, Nat Rev Drug Discov. 2006; 5(4):295-309), recent studies suggest that increasing cellular energy expenditure is an attractive alternative approach (Whittle et al. Trends Mol Med. 2011; 17(8):405-11; Boss et al. Front Endocrinol (Lausanne); 2012; 3:14).
Several biological mechanisms have been implicated in the development of obesity. For instance, the hormone leptin has been shown to regulate fat accumulation and eating behavior and numerous animal models of obesity have been established based on mutations in the leptin and leptin receptor genes. Obesity in turn has been implicated as a risk factor in diseases ranging from insulin resistance, type II diabetes, to metabolic syndrome, hypertension, cardiovascular disease, hyperlipidemia, sleep apnea, coronary artery disease, knee osteoarthritis, gout, infertility, breast cancer, endometrial cancer, gallbladder disease, colon cancer and lower back pain.
Currently available treatments for obesity are generally directed to suppressing appetite (diethylpropion tenuate, mazindol, orlistat, phendimetrazine, phentermine, and sibutramine), however these compounds may not be effective or appropriate in all subjects. Accordingly, new modes of treatment are needed and desirable. Treatments for diabetes are well known and include oral hypoglycemic agents such as sulfonylureas (tolbutamide, chlorpropamide and glibenclamide, biguanides (metformin and buformin), and α-glucosidase inhibitors (acarbose and voglibose). In addition, thiazolidinediones (troglitazone, rosiglitazone and pioglitazone), are commonly used to reduce insulin-resistance. However, thiazolidinediones are commonly associated with a weight gain and all anti-diabetic medications are associated with side effects. Thus, there is a still a need for more effective therapies for diabetes. We propose herein, agents and compounds modulating the expression of follistatin as therapeutics for the treatment or prevention of obesity, insulin resistance disorders and metabolic syndrome related disorders.
Follistatin binds to several members of the transforming growth factor-beta (TGF-β) family and blocks the interaction of these cytokines with their cognate receptors. Follistatin was first identified as a factor that could inhibit the release of follicle-stimulating hormone from pituitary cells (Ueno et al., 1987). It binds activins A, B and AB with high affinity and was also reported to bind activin E but not activin C (Nakamura et al., 1990; Schneider et al., 1994; Hashimoto et al., 2002; Wada et al., 2004). Follistatin-bound activin is unable to initiate signal transduction and consequently follistatin is a potent antagonist of physiological activin signals. Of the three follistatin domains present in all follistatin isoforms, (Shimasaki et al., 1988) the first two, but not the third, are necessary for activin A binding (Keutmann et al., 2004; Harrington et al., 2006). Aside from activins, follistatin also binds several bone morphogenetic proteins (BMP) including BMP2, BMP4, BMP6 and BMP7 (Iemura et al., 1998; Glister et al., 2004). In 2004 it was shown that follistatin binds myostatin (also known as growth and differentiation factor 8, GDF8) with high affinity and thereby is able to antagonize the inhibitory effect of myostatin on muscle growth (Amthor et al., 2004). Activin A is a critical component of the inflammatory response and follistatin can be used to block Activin A (Jones. et al. PNAS 2007).
The functional significance of the interaction between follistatin and angiogenin, a pro-angiogenic factor unrelated to the TGF-β family, remains to be determined (Gao, et al., 2007). The interaction of follistatin with heparin and heparin sulfates is isoform specific. For example, follistatin 288 binds to heparin sulfate, whereas this binding is blocked by the acidic tail of follistatin 315 (Sugino et al., 1993). Furthermore, myocytes and brown adipocyte cell lineages are interlinked, and this relationship between the cell lineages confirms a distinct origin of brown versus white adipose tissue. The relationship also provides an explanation, concerning the reason why brown adipocytes are connected with lipid metabolism rather than with energy storage. In that respect, brown adipose acts much like oxidative skeletal muscular tissue (Timmons, et al., PNAS, 2006). It has been determined that genes, including the muscle specific basic helix-loop-helix (bHLH) myogenic regulator myogenin, have been expressed in brown preadipocytes at a level which is comparable with differentiating confluent C2C12 myoblasts (Fulco et al. (2003) Mol Cell 12:51-62).
Brown adipose tissue (BAT) not only has a remarkable energy dissipating capacity but is also the most active tissue for promoting triglyceride clearance and glucose disposal and generates heat for thermogenic purposes (Bartelt et. al. Nat Med. 2011; 17(2):200-5). This specialized function of brown fat cells derives from high mitochondrial content and ability to uncouple cellular respiration through uncoupling protein-1 (UCP1) (Nedergaard et al. Cell Metab. 2011; 13(3):238-40.) The balance between white adipose tissue (WAT) and BAT affects systemic energy balance and is widely believed to be the key determinant during development of obesity and related metabolic syndrome (Kajimura et al. Cell Metab. 2010; 11(4):257-62; Nedergaard et al. Cell Metab. 2011; 13(3):238-40). Several lines of evidences suggest that BAT has anti-obesity function and that it protects from metabolic syndrome. Transgenic mice expressing UCP1 (a key BAT specific protein) under the control of fatty acid binding protein 4 (FABP4/AP2) promoter are resistant to genetic and diet-induced obesity (Hansen et al. Biochem J. 2006; 398(2):153-68). Targeted disruption of Cidea, which inhibits the uncoupling activity of UCP1, results in lean mice that are resistant to diet induced obesity (Zhou et al. Nat Genet. 2003; 35(1):49-56). Ectopic levels of BAT in mouse skeletal muscle have been shown to protect mice from high fat diet-induced metabolic syndrome with obesity, hyperglycemia, and insulin resistance (Almind et al. Proc Natl Acad Sci USA. 2007; 104(7):2366-71).
The prototypic androgens testosterone (T) and dihydrotestosterone (DHT) have been shown to up-regulate follistatin (Fst), an extracellular protein that binds activins and myostatin (Mst) with high affinity and inhibits TGF-β signaling in a variety of cell lines (Braga et al. Obesity, 2012 doi: 10.1038/oby.20117; Singh et al. Endocrinology. 2009; 150(3):1259-68; Braga et. al. Mol Cell Endo, 2012; 350(1):39-52). Considerable evidence indicates that inhibition of TGF-β/Mst/Smad3 signaling promotes a WAT to BAT phenotype change, mitochondrial biogenesis and protects experimental mice from diet-induced obesity (Braga et al. Obesity, 2012 doi: 10.1038/oby.20117; Yadav et al. Cell Metab. 2011; 14(1):67-79; Zhang et al. Diabetologia. 2012; 55(1):183-93).
Previous studies have suggested blocking preadipocyte to adipocyte conversion as an effective approach to regulate adipose tissue growth (Wu et al 2010). While differential screening was used to identify follistatin-like 1 (Fstl1) as a potential target in the adipocyte differentiation pathway, it was suggested that blocking Fstl1 expression would block adipocyte differentiation.
In contrast to such teachings, it is disclosed herein that up regulation of a follistatin domain containing protein (follistatin) is positively associated with brown adipose tissue differentiation and that compounds increasing follistatin expression can be utilized to treat or prevent an obesity related disorder. Therefore, the present invention is surprising and unexpected in view of the prior art and addresses the need for novel compositions, medicinal formulations, uses, methods, kits, and combination therapies capable of preventing or safely treating serious chronic diseases, and assays for identifying further compounds and compositions useful for the same.